The present invention generally relates to selective phase change ink compositions and to a process for applying same to substrates, and more particularly to the application and use of such inks in a process in which phase change compositions having selective process capabilities are applied to a substrate in indirect printing processes where intermediate transfer surfaces are employed.
In general, phase change inks are in the solid phase at ambient temperature, but exist in the liquid phase at the elevated operating temperature of an ink jet printing device. At the jet operating temperature, droplets of liquid ink are ejected from the printing device and, when the ink droplets contact the surface of the printing media, they quickly solidify to form a predetermined pattern of solidified ink drops.
The phase change ink comprises a phase change ink carrier composition which is combined with a phase change ink compatible colorant. Preferably, a colored phase change ink will be formed by combining the above-described ink carrier composition with compatible subtractive primary colorants. The subtractive primary colored phase change inks of this invention comprise four component dyes, namely, cyan, magenta, yellow and black. The subtractive primary colorants employed typically comprise dyes from either class of Color Index (C.I.) Solvent Dyes, Disperse Dyes, modified Acid and Direct Dyes, and a limited number of Basic Dyes.
Phase change ink is desirable since it remains in a solid phase at room temperature, during shipping, long-term storage, etc. Also, the problems associated with nozzle clogging due to ink evaporation are largely eliminated, thereby improving the reliability of ink jet printing. Furthermore, in prior art phase change ink jet printers where the ink droplets are applied directly onto the printing medium the droplets solidify immediately upon contact with the substrate, migration of ink along the printing medium is prevented and dot quality is improved. This is also true of the processes and ink compositions described herein.
The initial prior art on the direct application of phase change inks in ink jet printing involved monochrome inks jetted by electrostatic printing devices. Thus, for example, in U.S. Pat. No. 3,653,932, a low melting ink, 30 degrees Centigrade (.degree.C.) to 50.degree. C., is provided employing an ink base comprising diesters of sebacic acid. In a similar process, U.S. Pat. No. 3,715,219 describes another low melting point ink (30.degree. C. to 60.degree. C.) comprising a paraffin alcohol-based ink. However, when low melting point phase change inks are employed in printing onto a substrate, they exhibit offset problems, namely, when the printed substrates formed from these inks are stacked and stored for subsequent use, they can become adhered to one another, particularly if high ambient temperatures are experienced.
U.S. Pat. No. 4,390,369 and U.S. Pat. No. 4,484,948 describe methods for producing monochrome phase change inks which employ a natural wax ink base, such as Japan wax, candelilla wax, carnauba wax, etc., which is printed by direct application from a drop-on-demand ink jet device at a temperature ranging between 65.degree. C. and 75.degree. C. In U.S. Pat. No. 4,659,383, a monochrome ink composition is provided having an ink base comprising a C20-24 acid or alcohol, a ketone, and an acrylic resin plasticizer. These monochrome ink compositions are not durable and when printed by direct application can be smudged with routine handling and folding.
In Japanese patent application 128,053/78, amides which are solid at room temperature, such as acetamide, are employed as printing inks. U.S. Pat. No. 4,684,956 is directed to monochrome phase change inks utilizing synthetic microcrystalline wax (hydrocarbon wax) and microcrystalline polyethylene wax. This molten composition can be applied to a variety of porous and non-porous substrates using a drop-on-demand ink jet direct application technique.
EP 0177352 and EP 0206286 reference direct phase change ink jet printing in color. The ink bases for these systems comprise fatty acids, a thermoplastic polyethylene and a phase change material in the first application; and the alcohol portion of a thermal setting resin pair, a mixture of organic solvents (o- and p-toluene sulfonamide) and a dye in the second application.
In U.S. Pat. No. 4,830,671, a hot-melt or phase change color ink composition is provided having the properties of stability and uniformity of performance under ink jet printing conditions. The resinous binder for the above-described phase change ink is the condensation reaction product of one equivalent of polymerized fatty acid, two equivalents of diamine and two equivalents of a monocarboxylic acid.
In PCT publication WO 91/10711, a hot melt ink for direct application by ink jet printing is provided. The colored ink jet images have a relatively narrow melting range and inhibit crystallinity upon quenching to reduce attenuation of transmitted light. Phase change ink compositions for direct application onto an underlying substrate are described in U.S. Pat. No. 4,889,560, U.S. Pat. No. 4,889,761, U.S. Pat. No. 4,992,304, U.S. Pat. No. 5,084,099, all of which are assigned to the assignee of this patent application, and all of which are incorporated herein by reference in pertinent part.
The carrier composition of phase change inks preferably includes a fatty amide-containing compound. It may also include plasticizers and tackifiers. Thin films of substantially uniform thickness of this ink composition are rectilinearly light transmissive, so that the inks are suitable for preparing overhead transparencies when used in the manner described in the patents just referenced above.
All of the above-described prior art relates to direct phase change ink processes in which the ink is jetted in the form of discrete drops directly onto a substrate. In prior art phase change ink systems, such as U.S. Pat. No. 4,889,560, special selective process capabilities are not required because the phase change ink is applied directly to the substrate by the use of an ink jet printing process. However, phase change inks which work in direct processes do not necessarily perform satisfactorily in indirect processes where the inks are first applied to an intermediate transfer surface and then to the final receiving substrate or surface. These problems are solved by the present invention which relates to phase change ink compositions with selective process capabilities.